here in the midwest, several young girls went missing. some were found murdered. others were never found at all. lori dupies, 20, wisconsin. reyna ricin, 14, from laporte, indiana, wendy felton, 16, from marian, indiana, michelle dewy, 20, in indianapolis, indiana. all of these cases went unsolved. officials believed only one man knew what happened. >> we knew he was responsible for several deaths. >> and to get answers, it would take a risky, unusual plan, send a convicted drug dealer undercover into a dangerous prison to befriend an alleged serial killer. >> i'm not a serial killer hunter. i said how am i going to do this? >> at stake, answers.